Patent GB-1500977-A (GB)
Title: Exposure control apparatus
IPC: G03B7/0805
Filed: 1975-06-10
Abstract: 1500977 Camera exposure control CANON KK 10 June 1975 [10 June 1974] 24755/75 Heading G2A A camera has means for generating a digital brightness signal, means for generating a digital signal corresponding to a manually set shutter speed, a diaphragm pre-setting member 303 coupled to a scanner Ra, which, upon movement of the presetting member, moves across a series of contacts Ra to produce a number of pulses dependent on the movement of the pre-setting member, and a computer which computes a required diaphragm stop from the digital signals and arrests movement of the diaphragm pre-setting member 303 when the number of pulses generated indicates that the diaphragm has been set to the computed stop. As described, the camera is operable in four modes. (1) Manually selected shutter speed, automatically determined diaphragm aperture. A ring 301 is set to EE to select auto diaphragm and thereby close switches SP, SP'' and SD (see Fig. 2). A dial A is set to the required shutter speed. On pressing release 347 a switch SRI is closed to energize an electromagnet Mgl which moves a pawl 313 to free a release lever 314. Lever 314: (a) Opens a memory switch Sm so that a digital signal Br dependent on object brightness measured by a cell 346 is memorized in a register 51. An adder 6' adds Bv to a digital signal Sv and a subtracter 7' subtracts a digital signal Tv so that a register 12' stores Bv + Sv - Tv. (b) releases a latch 316 which frees a gear 318 to (i) drive a diaphragm pre-setting ring 303 clockwise via linkages 329, 303c and (ii) move a contact scanner Ra, over a series of spaced contacts Ra to generate a pulse at each pair of contacts. The pulses generated by a circuit 10', Fig. 2, are stored at 11' and compared at 9' with the signal Bv + Sv -Tv at 12'. When equal an electromagnet Mg2 is energized to halt gear 318 and thus halt diaphragm ring 303. (c) releases a latch 315 which allows the diaphragm to stop down and the mirror 338 to swing up. A delay circuit 8' (which ensures that the mirror is up) then energizes an electromagnet Mg3 to open the shutter and a timer 14' controlled by the pre-set speed Tv energizes an electromagnet Mg4 to close it and to return the mirror and open the diaphragm. (2) Manually selected diaphragm aperture, automatically determined shutter speed. Ring 301 selects the desired aperture, did A is set to EE which closes ST, ST'. On release, lever 314 (a) opens memory switch SM, so that Bv and Sv are fed to circuit 7'. (b) releases latch 316 which frees gear 318 to (i) drive ring 303 until it reaches the pre-selected stop (ii) move contact Ra, so that circuit 10' generates a corresponding digital signal Av. Circuit 7' thus receives Bv + Sv - Av = Tv and this is stored at 12'. (c) releases latch 315 to operate the mirror and diaphragm. Delay circuit 8' releases the shutter as before, exposure being controlled.by timer 14' which is connected to store 12' by switch ST'. (3) Manually selected shutter speed and diaphragm aperture. The selected values are set, and switch SW is closed. On shutter release, ring 303 moves to the selected stop value, when timer 8' releases the shutter, exposure time is controlled by circuit 14' connected by SW to the selected value Tv. (4) In the fourth mode, a shutter speed Tv is manually selected on dial A, a button 501 is pressed to open memory switch Sm and to release latch 316, and ring 301 is manually turned step by step to alter the diaphram and via contacts Ra to generate a corresponding digital signal Av. Comparator 9 compares Av with Tv and Bv and energizes an indicator lamp L when the correct aperture is reached.